
Light novel knowledge here. :Spoilers:
You're right on the nose about her fever. It is caused by latent magical ability. Unfortunately, its not as simple as one day she wakes up able to cast fireballs and her fevers are gone. Magic is actually really really rare, especially among the peasantry. Most people with "the devouring" die short and painful lives. If you have a strong will, like main does, you can push back by controlling your emotions for a awhile, but eventually it'll become too much. A temporary solution is to use a magic tool, any magic tool, to release pent up mana, but the mana then builds up again faster than before. Most magic tools are in the hands of nobles, passed down as family treasures. If you have connections and money, you can rent tools, but the more common solution is for suffering individuals to enslave themselves to nobles for the right to use tools.
Eventually, this is a choice main must face; enslave herself or die among her friends and family.

oh, i didn't expect that. I did expect that magic is extremely rare, especially among commoners, I thought it was being foreshadowed with the writing and books, but not to this extinct. it gets kinda depressing( ̄∇ ̄")
the harsh reality just slaps you in the face, kicks you it the stomach until you are down and then some more (/TДT)/
but I bet main will think of something, like she always doesヾ(❀╹◡╹)ノ~
maybe she will choose enslavement but with a clever condition (like telling how to make paper or printing methods or some other knowledge from her past life to buy her freedom back) or will make her own magic tool or she will be able to fix a broken tool(if it were something also connected with books in some way it would be even better).
at least I hope she does something along those line, because like I said, her resourcefulness and hard work, her will to not give up against all odds is one of greatest charms of this manga, at least for me ٩(๑❛ᴗ❛๑)۶
thanks for the spoilers(づ ̄ ³ ̄)づ

I'd recommend you read the novel cause I don't want to spoil. Let's just say I cried a couple times. And I don't know how certain characters haven't killed her yet. She is waaaay too naive about some things. Especially where books are concerned (she gets tunnel vision and gets into all kinds of trouble). I love books too...but dang girl
I am talking about her fever. in ch 13 we learn something new about her fever:
http://www.mangago.zone/read-manga/ascendance_of_a_bookworm/nbt/c012/pg-13/
we already knew it is related to her emotions, especially the extreme ones, but it seems she can control the fever (kinda, just a bit). what if that fever is actually her unreleased magical power, and that is the reason she is so fragile? I think there were similar symptoms in other manga for young children with large magical abilities.
I feel conflicted. on one hand, I love the current story, without magic, it's so interesting and has a great flow, showing hard work and resourcefulness of the MC to an amazing but still believable degree, with a bit of slice of life, making it even more charming. on the other, it could be interesting to see what she would do if she actually has magical powers, how she would use them - probably to work for/with nobles so she could finally get her beloved books ╮( ̄▽ ̄)╭. Ether way, I just hope the quality of the story will continue to be as high as it is now, and won't become generic and cliche. not that it's anything wrong with that, I like them too, just that this manga has so much potential in would be a waste if it would loose it's uniqueness ٩(๑❛ᴗ❛๑)۶